Reverse String II

Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are fewer than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.

Example:

Input: s = "abcdefg", k = 2
Output: "bacdfeg"

Approach

Java

package com.practic.string;

public class ReverseStringII {
    public static void main(String[] args) {
        String s = "abcdefg";
        int k = 2;
        System.out.println(reverseStr(s, k));
    }

    static String reverseStr(String s, int k) {

        int n = s.length();
        if (n == 0 || k == 0)
            return s;
        int i = 0;
        while (i < n) {
            s = reverse(s, i, +Math.min(i + k, n)-1);
            i += 2 * k;
        }
        return s;
    }

    private static String reverse(String s, int i, int j) {
        char[] cS = s.toCharArray();
        while (i < j) {
            char c = cS[i];
            cS[i] = cS[j];
            cS[j] = c;
            i++;
            j--;
        }
        return new String(cS);
    }

}

C++

#include <bits/stdc++.h>
using namespace std;

string reverseStr(string s, int k)
{
    int n = s.size();
    if (n == 0 || k == 0)
        return s;
    int i = 0;
    while (i < n)
    {
        reverse(s.begin() + i, s.begin() + min(i + k, n));
        i += 2 * k;
    }
    return s;
}

int main()
{
    string s = "abcdefg";
    int k = 2;
    cout << reverseStr(s, k);
    return 0;
}